Whale Back Rock EarthCache
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Waypoint 9 of 10 on Going Coastal’s NY-NJ Harbor Estuary Earthcache Discovery Trail in Inwood Hill Park, caches developed by Going Coastal, Inc. (www.goingcoastal.org) as a special project in affiliation with Groundspeak and support from the NY-NJ Harbor Estuary Program and the New England Interstate Water Pollution Control Commission.
The NY-NJ Harbor Estuary Earthcache Discovery Trail is meant to help visitors develop a better understanding of the Estuary, make connections between earth and environmental science, and foster stewardship.
Whale Back Rock tells the story of glaciation in Inwood Hill Park. It can even tell you which way the glacier flowed. From this cache you can see a tremendous span of geologic time. You can also see evidence of the geologic processes that created the rocky Inwood Hill. (visit link)
As glaciers move, they pick up anything in their path, from small grains of sand to gigantic boulders. Objects carried by the ice act like bulldozers plowing sediment and wearing down all objects in the glaciers path. A glacier will even change the shape of mountains as it passes through. (visit link)
Whale Back Rock is an outcrop of Manhattan schist polydeformation or refolding of re-crystalized pre-existing rocks by retrograde metamorphism.
The boulder was later rounded and polished by glaciers, leaving linear scrape marks, called striations. Stand on the rock to see them. By mapping the direction of the marks, you can tell which way the glacier was moving.
Did you ever wonder where rocks come from? How is a rock made? Rocks are classified based on how they originated.
All rocks are made of minerals. But you don't need rocks to make minerals. There are three main classes of rocks – (1) Sedimentary, (2) Igneous and (3) Metamorphic.
Sedimentary rocks began as mud and sand. These are called sediments. As the layers of sediment build up over millions of years and are weighted down by more sediment, the bottom layers harden together.
Igneous rocks, from the Latin word igneus meaning of fire, forms when lava or magma cools.
Metamorphism of sedimentary rocks forms from extremely powerful collisions and temperatures deep inside the earth. Whale Back and the rock shelters of Manhattan schist are metamorphic sedimentary rocks.
Just like butterflies go through metamorphosis when they enter their cocoons as caterpillars and emerge as butterflies, the rock emerges changed.
When rocks break down the eventually turn to sand. This rock cycle never stops. (visit link) When Earth's tectonic plates move around, they produce heat. When they collide, they build mountains. Pressure and heat inside the earth metamorphose the rock. Weathering and erosion eventually break up rocks and washes away the sediment. This new sediment in turn forms sedimentary rock.
How do you tell the different rocks apart? All rocks are made of minerals, nonliving crystals. But, not all rocks are the same. Manhattan schist minerals have shiny flakes, often mica and red garnet. A closer look and you will see the gems sparkle. Inwood marble is white and grainy like sugar; it is made of limestone formed from dead sea creatures. Thick beds of marble lie below the Harlem River, a vein is exposed under the Henry Hudson Bridge and at nearby Isham Park. The minerals in ancient Fordham Gneiss are laced together in ribbons of lighter and darker bands of color.
Logging Tasks:
1. Whale Back is as wrinkled like a Sharpei dog and is pockmarked. Name one rock formation process and one geologic event that gave Whale Back its ruddy surface texture.
2. Look closely at the rock. There are foliations going in one direction and striations in another along the top. From observing the striations can you tell the direction the ice sheet travelled?
3. If glacial striation is found in a temperate climate zone like New York, what can we infer about how climate changed over time?
4. (Optional) Whale Back rock has been smoothed by glaciers and weathered by time. As the rock erodes in Inwood Hill, what path will the sediment travel. Map the possible trail of a sediment particle on its travels from Inwood Hill to where it might eventually end its journey. (POST TO LOG)
To log a find on this earthcache, email the cache owner (DO NOT POST IN YOUR LOG) unless otherwise directed. Use your GPS device to locate the next cache - GC2RWRK. (visit link)
Remember, to upload a photo and let us know in your log ways we can improve the trail.
Data Sources:
• U.S. Geological Survey: (visit link)
Data Collected: September 26 – April 15, 2011
Name and Type of Land
Inwood Hill Park
W 218 Street & Seaman Avenue, Manhattan
Phone: (212) 304-2365
www.nycgovparks.org
Owner: NYC Department of Parks & Recreation
Additional Hints
(No hints available.)